The Role of Surface Condition in the Yields of Secondary Electrons, Backscattered Electrons, and Photoelectrons From Spacecraft

This paper reviews some active research topics of outgoing electron currents in spacecraft charging. The spacecraft potential is determined by the current balance. On a spacecraft, the incoming currents of ambient electrons and ambient ions can be measured, whereas the outgoing currents of secondary electrons (SEs), backscattered electrons (BEs), and photoelectrons (PEs) cannot. The outgoing currents depend on the incoming currents, surface materials, and surface conditions. For SE yields, using the encyclopedia parameters of the materials is not sufficient; surface conditions also need to be taken into account. For BEs, the yield approaches unity as the primary electron energy approaches zero. For PEs, reflectance is important. We conjecture that highly reflective surfaces generate little or no PEs and would charge to negative voltages as if in eclipse. As a consequence, differential charging may develop between adjacent surfaces as they get exposed to sunlight.